The Gulf of Mexico dead zone: What causes it, and what could fix it

Seated at the mouth of the Mississippi River, the Gulf of Mexico receives everything that flows through the river — which includes more than just water.

Sediment, runoff, and nutrients all deposit into the Gulf of Mexico, sometimes originating as far north as Minnesota. The large number of pollutants entering the outlet causes massive problems, sometimes in ways that one would not expect. For example, it might be surprising to learn that a large inflow of nutrients like nitrogen and phosphorus have adverse consequences for the ecosystem of the Gulf of Mexico.

When an excess of nitrogen and phosphorus enter a large body of water, an algal bloom occurs. As these algae blooms grow, two things happen: the algae on the surface prevent light from reaching aquatic plants below the surface, causing these plants to die, and the algae also die. Bacteria break down the dead organisms, a process that requires the use of oxygen. This results in a deficit of oxygen, creating a dead zone where plants and animals cannot exist.

Such a dead zone exists in the Gulf of Mexico, and it is at its largest size since measuring began in 1985 — roughly the size of New Jersey. The large size is concerning considering the massive impacts the dead zone has on the Gulf of Mexico and the Gulf Coast area.

Besides disrupting the ecosystem, the dead zone poses economic problems to the area. Seafood is a large industry in the region, and fish kills represent a major threat to this industry.

The dead zone is projected to grow, and it certainly will not shrink without some sort of change occurring.

One way to reduce the amount of nutrients that reach waterways is to implement nutrient removal techniques in wastewater treatment facilities.

In Washington, D.C., DC Water has introduced enhanced nitrogen removal facilities that allow the Blue Plains treatment plant to significantly reduce the amount of nitrogen discharged into the Potomac River; they claim that these new facilities have prevented over 144 million pounds of nitrogen from entering the Potomac River.

DC Water is also constructing a new tunnel system that will prevent sewer overflows from being flushed into waterways without first being treated. With rising concerns over excess nutrients in water ecosystems, wastewater treatment facilities around the United States are facing pressure from local, state, and federal governments to implement nutrient removal processes similar to those utilized by DC Water.

Besides discharges from wastewater treatment plants, runoff also represents a major source of nutrients in waterways. Phosphorus and nitrogen are the main components of fertilizers and make their way into rivers, lakes, and other bodies of water as a part of agricultural runoff. Runoff is classified as a non-source pollution and is therefore unregulated, so it has been difficult to track and prevent the amount of nutrients entering waterways through this route.

However, this does not mean that it is impossible to reduce the amount of runoff that reaches bodies of water.

Investing in green infrastructure can prevent an abundance of nutrients in waterways and has other benefits like reducing flooding. Green infrastructure includes rain gardens, bioswales, permeable pavements, and rainwater harvesting. Incorporating green infrastructure alongside traditional infrastructure can help reduce the amounts of nitrogen and phosphorus reaching waterways.

The UC Davis Renewable Energy Anaerobic Digester, which officially opened Earth Day, April 22, 2014, converts organic waste from campus and other sources into clean energy for the campus electrical grid. The anaerobic digestion technology used in the facility was invented by UC Davis professor Ruihong Zhang and licensed to Sacramento-based CleanWorld. (UC Davis)

An aerial view of Prime Hook National Wildlife Refuge in Milton, Delaware. Wetlands, like those shown here, has many benefits for a bay's ecosystem, including filtering runoff, mitigating floods, and as a home to baby fish and invertebrates. (Photo courtesy U.S. Fish and Wildlife Service)